1. Field of the Invention
The present invention relates to solar power, and, more particularly, to running DC loads by use of solar power.
2. Description of the Related Art
Current solar photovoltaic (PV) systems for residential and commercial buildings typically produce direct current (DC) which is inverted to alternating current (AC) using inverters in and connected to an AC circuit breaker box within or on the building. Such systems suffer from power intermittency caused when the grid must make up any short term reduction in PV output. Current HVAC systems such as heat pumps often utilize AC-to-DC-to-AC, AC motor controls or AC-to-DC power supplies especially when the fans or compressors have variable-speed motors. There are a variety of variable-speed motors which could utilize DC input. Examples are brushless DC motors (BLDC motors) also known as electronically commutated motors (ECM), as well as variable-frequency drives (VFD) for AC motors, which may also be configured to use DC as the input to the VFD. For example, a Bosch brand geothermal heat pump uses AC-to-DC power supply to power a variable speed ECM fan motor. For the purposes of this invention description, the phrase “DC motor” refers to any motor system where DC is the PV input to the motor or motor controls, even in the case of a DC input VFD controlling a variable speed AC motor or similar.
It is known to convert all of the DC from PV to AC for use by AC building loads or for export to the utility grid. What is not known in the conventional art is to adjust DC loads such that the DC loads consume a maximum amount of the DC electrical output of the solar panels, and to convert DC power from solar panels to AC only if all of the DC power is not being consumed by a DC load. Moreover, it is not known to purposefully manage loads, in a variable manner, on the demand side of the meter in concert with the variability of PV power for the purpose of reduction in or avoidance of power intermittency on the grid. Further, it is not known in the conventional art that the DC load is in the form of an HVAC system, such as a heat pump with DC input to the DC phase of AC-DC-AC motor controls.